The present invention relates to a braking system for braking a rotor relative to a stator, said system comprising brake disks disposed in a disk enclosure, which disks are distributed in a first series of disks secured to the stator and in a second series of disks constrained to rotate with the rotor relative to the stator, the system further comprising a brake piston device that can be caused to go between a braking configuration in which an active portion of said piston device co-operates with the brake disks so as to urge said disks into braking contact, and a brake release configuration, the system further comprising control means for controlling the piston device, which control means comprise braking resilient return means continuously urging the brake piston device towards its braking configuration, a brake release chamber distinct from the disk enclosure and suitable for being fed with pressurized fluid via a brake release duct so as to urge the brake piston device into its brake release configuration, and a braking chamber suitable for being fed with pressurized fluid so as to urge the brake piston device towards its braking configuration, the braking system further comprising a cooling device for cooling the brake disks by means of fluid flow.
Such a braking system is a multi-effect braking system. It makes it possible to provide parking and emergency braking by means of the presence of the braking resilient return means which make braking possible when the brake release chamber is not fed with pressurized fluid to an extent sufficient to increase in volume by overcoming the braking resilient return force. It also makes it possible to provide in-service or dynamic braking which serves to decelerate and to brake a vehicle driven by a motor including the braking system, under the effect of fluid being fed to the braking chamber. Thus, the brake disks are suitable for absorbing the energy produced on decelerating and stopping the vehicle.
It is known, e.g. from patents US 3 927 737 and US 3 946 837, that it is necessary to irrigate the brake disks of such a multi-effect brake with a cooling fluid. The cooling is achieved by a flow of fluid fed via a specific cooling duct that opens out in the disk enclosure. The flow of cooling fluid is removed to the outside of the casing of the braking system via another duct connected to a fluid return.
Thus, the casing of the braking system must be provided with two orifices for the cooling fluid circuit, an orifice for the brake release duct that feeds the brake release chamber, and an orifice for the braking duct that feeds the braking chamber. Four holes, each of which is connected to a specific fluid duct, are necessary since each of them needs special treatment. This increases production costs and complicates management of the braking system.
A braking system of the above-mentioned type is also known from EP-A-0 913 304, in which a tapping duct continuously connects the brake release chamber to the disk enclosure. The tapping duct is formed in a valve device which serves to facilitate emptying the brake release chamber when emergency in-service braking is necessary. The fluid tapped continuously from the brake release chamber serves to lubricate and to cool the brake disk assembly.
The tapping duct is disposed inside the braking system, between the brake release chamber and the assembly of disks. It can be accessed only by disassembling the brake. Maintenance operations are therefore difficult, lengthy, and costly.
An object of the present invention is to propose a braking system that is simplified compared with the above-mentioned prior art systems, and that overcomes the above-indicated drawbacks.
This object is achieved by the facts that, for the purpose of being fed with cooling fluid, the cooling device is provided with a cooling duct branching from the brake release duct and communicating with the disk enclosure, that the cooling duct is formed in a casing portion of the braking system, and that it is provided with means for limiting the quantity of cooling fluid tapped by the cooling duct from the brake release duct.
The cooling duct branches from the brake release duct, so the casing of the braking system is provided with a single orifice for feeding both the cooling circuit and the brake release chamber (an orifice further being provided for feeding the braking fluid with fluid). However, the cooling duct is connected to the brake release circuit upstream from the brake release chamber.
Cooling fluid flow depends on brake release fluid feed. In other words, cooling ceases when brake release is no longer effective, which is functional since the source of heating also ceases when the rotor stops rotating. In contrast, during the deceleration phase, the brake release chamber continues to be fed, so that the brake disks continue to be irrigated with cooling fluid.
In addition, the continuous flow of fluid in the brake release circuit makes it possible to maintain the temperature of the fluid at a value such that its viscosity is sufficiently low, e.g. lower than 40 cSt, to ensure that the interruption in brake release by emptying the brake release chamber takes place with a short response time, of about 0.2 seconds, even if the ambient temperature is low, e.g. lower than 0xc2x0 C.
Compared with the braking system of EP-A-0 913 304, the braking system of the invention makes it possible to provide maintenance that is greatly simplified since, in order to access the cooling duct, it is not necessary to disassemble the brake, nor even the brake release duct assembly. The cooling duct is formed in a casing portion and it is not necessary to disassemble parts internal to the braking system in order to have access to it.
Advantageously, the cooling duct is connected to the brake release duct via a connection segment which is formed in a casing portion and which has an end that is situated at the outer periphery of said casing portion and that is closed by removable closure means.
In which case, to access the cooling duct, it is necessary merely to remove the closure means.
In addition, the quantity of cooling fluid tapped from the brake release duct is limited by the means provided for this purpose, so that tapping cooling fluid does not adversely affect brake release.
Advantageously, the cooling duct is connected to the brake release duct via a device for limiting the flow rate of the fluid through said cooling duct.
This device for limiting the flow rate constitutes simple means for limiting the quantity of cooling fluid tapped from the brake release duct.
The flow-limiting device is preferably situated in said connection segment. Thus, maintenance operations (cleaning, replacement, repair) on the flow-limiting device can be performed after merely removing the above-mentioned closure means. The flow-limiting device can even be implemented in the form of interchangeable cartridges disposed in the connection segment (which is preferably rectilinear). Various cartridges may be used to satisfy various conditions of use for the brake.
Advantageously, the flow-limiting device is provided, at least in part, in the closure means which are disposed so as to be interposed between the brake release duct and the outlet of the cooling duct in the braking system.
Thus, on the basis of xe2x80x9cstandardxe2x80x9d manufacture, it is possible merely to change the closure means in order to adapt the flow-limiting device to suit the conditions under which the brake is to be used.
The flow-limiting device is advantageously constituted by a restriction via which the cooling duct is connected to the brake release duct.
Advantageously, the cooling duct is connected to the brake release duct via a calibrated valve that allows the fluid to flow from the brake release duct to said cooling duct only when the fluid pressure in the brake release chamber is at least equal to a determined pressure.
The calibrated valve makes it possible to prevent the tapping of the cooling fluid from causing the pressure to drop in the circuit for feeding the brake release chamber with fluid. In addition, it makes it possible optionally to effect brake release with a pressure lower than the calibration value of the valve, without causing any cooling fluid to flow.
The presence of the calibrated valve or, more generally, of a flow-limiting device comprising means for automatically preventing the cooling duct from being fed with fluid, makes it possible to avoid a major drawback of the prior art described in EP-A-0 913 304. That drawback lies in the fact that, since the fluid is tapped continuously from the brake release chamber via the tapping duct, a reduction in the pressure in said chamber (due, for example, to a minor malfunction of the fluid feed means) might cause unwanted braking. Tapping the fluid empties the brake release chamber and amplifies the pressure reduction. It should also be noted that the fact that such a calibrated valve or that such automatic means can be disposed in the cooling circuit which is itself situated in a casing portion facilitates maintenance of the valve or of said means.
This is advantageous in particular when it is necessary to effect emergency brake release so as to be able to tow the machine equipped with the braking system of the invention. In which case, the pressure that makes brake release possible is in general delivered by an emergency auxiliary fluid source, such as a pre-charged pneumatic oil accumulator, an emergency electrically-driven pump set, a hand pump, or some other source. The flow rate of fluid delivered by such a source is relatively low, and the presence of the calibrated valve makes it possible to avoid it being necessary to xe2x80x9cuse upxe2x80x9d fluid unnecessarily for cooling which is of no utility when towing.
A hydraulic motor comprising a rotary cylinder block having radial pistons and disposed in a stationary casing having a reaction member for the pistons advantageously further comprises a braking system of the invention, the rotor and the stator of said system being constrained to rotate respectively with the cylinder block and with the casing of said motor.
The stationary-casing motor may, for example, drive one or more displacement members (wheels) of a vehicle. The casing is fixed to the frame of the vehicle, while the cylinder block is coupled to the wheel via a shaft.
The multi-effect braking system makes it possible, during dynamic braking, to cause the vehicle to undergo gradual deceleration.
In such a motor, the disk enclosure is advantageously connected to the space inside the motor that is provided between the casing and the cylinder block via non-return valve means allowing the fluid to flow only in the direction going from the disk enclosure towards said inside space.
The inside space of the motor is normally filled with a fluid at a limited pressure, in particular under the effect of leaks that occur in the cylinder block. The cooling fluid is caused to flow simply by ensuring that the fluid flows into the inside space of the motor after it has passed through the disk enclosure. Generally, the inside space of the motor is connected to a pressure-free tank via a leakage return duct. In this way, the leakage return duct of the motor is used to remove the cooling fluid. This layout is advantageous because it makes it possible to omit a connection to a fluid return in the braking system and also the corresponding duct in the casing of the braking system, which connection and duct would otherwise be necessary to remove the cooling fluid.
When the motor includes a drive motor that is constrained to rotate with the cylinder block and a leakage return duct that connects an internal enclosure of the motor to an external discharge enclosure, the disk enclosure advantageously communicates with said internal enclosure via a connection duct provided in the drive shaft. This internal enclosure is distinct from the inside space of the motor that is provided between the cylinder block and that portion of the casing of the motor which has the reaction cam.
In which case, the connection duct provided in the drive shaft is of extremely simple shape. A motor is thus obtained that is compact and that is provided with a multi-effect brake, in which the cooling circuit makes use of the existing leakage return duct of the motor and is connected to it by a configuration that is simple and low-cost by means of the connection duct bored through the drive motor.
In an advantageous variant, the motor includes at least one group of pistons that are suitable for being xe2x80x9cdeclutchedxe2x80x9d by being retracted into their respective cylinders towards the axis of rotation of the motor, said pistons being suitable for being maintained in this declutched position by the fluid pressure prevailing in the inside space of the motor that is provided between the reaction member and the cylinder block, said inside space being connected to the leakage return duct via calibrated valve means. The disk enclosure is then advantageously connected to the inside space of the motor so that the pressure serving to maintain the pistons in the declutched position is provided by the fluid coming from the disk enclosure.
By means of this configuration, the cooling fluid is used to contribute to maintaining the pistons in the declutched position, without requiring the presence of a duct fed specifically for this purpose. For example, the calibrated valve means may comprise a valve set to about 2 bars.